158 



DEVELOPMENT OF ORGANIC LIFE 



[Ch. IX. 



the plover, have been observed in rocks of higher anticmif 

 in North America.** These bipeds have left the marks f 

 their footsteps on strata of Triassic age in the valley of th 

 Connecticut, and they are useful in warning us against sw 

 culating on the relative grade of ancient and modern repre 

 sentatives of this class, seeing that, although there were 



many of 

 Hitherto 



search in all formations older than the Trias, so that we may 

 declare at present that the first appearance of fish, reptiles 

 and birds, follows a chronological order in accordance with 



same 



ranged zoologically by a naturalist in an ascending series • 

 and we shall presently see that the lowest class of Mammalia 

 have not yet been traced back so far as the footprints of the 

 earliest known birds. 



Mammalia. — So late as the beginning of the present cen- 

 tury it was a generally received dogma in geology that the 

 Mammalia had not been created before the Tertiary period, 

 and the first announcement of the discovery in the Lower 

 Oolite of Stonesfield, of the jaw of a small marsupial, recog- 

 nised as such in 1818 by Cuvier, caused a sensation almost 

 as great as would now be excited by our finding the bones of 

 some quadrumanous animal in one of the Secondary rocks. 

 Many naturalists, rather than allow their faith in the theory 

 of progressive development to be so rudely shaken, cherished 

 to the last a hope that it might ultimately turn out that the 

 British geologists had been mistaken in their opinion as to 

 the age of the deposit in which this precious relic was en- 

 tombed : while other eminent anatomists, M. Blainville among 

 the number, called in question the mammalian character of the 

 relic. But no less than nine other specimens of lower jaws 

 of mammiferous quadrupeds have since been met with in the 

 same slate of Stonesfield. so that, including the first found 

 (fig. 3, p. 159), there are now four distinct species referable 



3nera in this one member of the Lower Oolite. 



After Cuvier had referred the specimen first met with to a 



* See Hitchcock's Eeport on Geol. of Massachusetts, and LyelFs Travels in 





North America, chap. 12. 



